1. Field of the Invention
The present invention relates to a suspension device for a vehicle seat (especially for an automotive seat), and particularly is concerned with a suspension device of this kind which is provided with a weight adjusting mechanism.
2. Description of the Prior Art
There has been available a seat suspension device of the type equipped with a weight adjusting mechanism for the purpose of enabling an occupant to adjust an optimum seating height of the seat according to his or her weight.
The suspension device of this kind is interposed between the seat and floor of an automobile, comprising a base lower frame fixed on the floor, a movable upper frame fixed to the seat, an elastic torsion bar provided between the two lower and upper frames, and an adjusting means for adjustably varying the repercussive force of the torsion bar to effect the weight adjustment.
In this ordinary structure, a downward load, i.e. a weight of the occupant, is directly applied to the torsion bar. However, the torsion bar per se, which is generally employed in this suspension device, is limited in tolerable amount of load absorbing rate, providing as small as about 90 kg/15 mm for weight adjustment range. To compensate for this deficiency, it might be proposed that the torsion bar is formed greater in thickness or diameter, but it will impair a cushioning effect of the seat suspension device and also require a greater force to operate the adjusting means in adjusting the repercussive force of the torsion bar according to the weight of the occupant. Consequently, this conventional suspension device has remained defective in its operationability and cushioning effect.